Dual concentric pipes

ABSTRACT

A dual concentric pipe string for bore hole coring having inner and outer concentric pipe sections, the outer pipe sections being secured together by the usual threaded connection, the inner pipe sections being connected through coupling devices containing elastomeric bodies that make a friction fit with the end portions of adjacent inner pipe sections, the inner pipe sections being frictionally secured to longitudinally spaced elastomeric centralizers having circumferentially spaced longitudinal ribs engaging the inner wall of the outer pipe sections to maintain the inner sections coaxial of the outer sections, with some of the centralizers engaging transverse shoulders in the outer sections to secure the inner sections in the outer sections against substantial longitudinal movement with respect thereto.

This is a division, of application Ser. No. 392,628, filed Aug. 29, 1973and now U.S. Pat. No. 3,871,486.

In the drilling of bore holes into the earth, it is desirable to havesamples of the formation being drilled on a continuous basis, so thatthe formation samples may be examined for various purposes, as thedrilling progresses.

Heretofore, efforts to continuously take a core sample from the bottomof the bore hole, while drilling with mud, have resulted in reduceddrilling efficiency and problems of cuttings removal. Dual concentricdrill pipes have been utilized to conduct the drilling fluid from thesurface to the drill bit in the drill pipe annulus, the fluid returningthrough the inner drill pipe to carry core samples to the top of thebore hole. However, inefficient cuttings removal in the bore holeannulus may result in the drill string becoming stuck, and the coresamples may also stick in the inner drill pipe, if the fluid velocity islow. In addition, the core samples have been contaminated with debrisfrom the bore hole which may be reground. In the absence of highvelocity fluid carrying of the core samples, moreover, gravityseparation of sample particles of different size or weight precludes thesamples recovered at the top of the bore hole from being representativeof the formation at any given time. Such problems are even greater whendrilling with air and a percussion bit.

The present invention provides a novel system and apparatus for moreefficiently drilling a bore hole while continuously taking core samples,using an airhammer and percussion bit.

More particularly, the present invention provides a novel system andapparatus whereby the core samples are taken at the center of the bottomof the bore hole and are protected against contamination by side wallmaterial. The drilling fluid velocity which carries the core samples tothe top of the bore hole is high, so as to minimize gravity separationof the core sample particles of different weight or size, so that thesamples are representative of the formation at any given time duringdrilling. In addition, the drilling fluid which carries the othercuttings to the surface is of sufficient volume and velocity as toprevent fall out and regrinding of material at the bottom of the borehole.

The entire system of the invention consists of a continuous coringadaptor swivel assembly, a continuous coring airhammer drill, completelyintegrable with any existing top drive or table drive rig for drillingbore holes, employing a rotatable drill pipe and air as the flushingfluid.

In its basic operation, compressed air is moved through the continuouscoring adaptor swivel, down the annulus of the double-walled continuouscoring drill pipe, to the coring airhammer. In the hammer, thecompressed air is divided in such a way as to allow the major part, sayapproximately 90%, of the energy derived from the air flow, to properlyrun the coring tool. This air is exhausted from the tool at the bit faceand allowed to return to the surface in the outer bore hole annuluscarrying a major portion of the cuttings as in conventional airhammerdrilling processes. The remainder of the air is diverted through thehammer and enters the core receiving tube just above the bit face athigh pressure and velocity. Formation cores and smaller chips are pickedup by the air in the core tube and carried through the inner tube to theadaptor swivel at the surface where the core samples are removed andcollected in any suitable fashion, such as a vortex type separator.

The continuous coring adaptor swivel of the invention, is adapted forapplication to any existing top drive or table drive rotary drillingrig. When in place, the swivel offers no interference to ordinarydrilling operations, In addition, the swivel affords easy access to fullflow reverse circulation, at high pressure, in the event the drillstring becomes stuck in the bore hole.

The continuous coring adaptor pipe or dual concentric drill pipe, is ofa standard size in use on conventional rigs and all tool joints arestandard, and the core tube does not interfere with conventionaldrilling. The core tube is securely held within the outer pipe andcannot accidentally come out during handling, but the core tube is freeto move longitudinally with respect to the outer pipe, as may benecessary for making up and breaking out joints of the drill pipe, sayduring round tripping to replace a bit. The pipe assembly is such thatenergy transients causing vibration in the core tube are dampened withrespect to the outer pipe.

The continuous coring airhammer structure of the present system, ingeneral, is constructed to develop high horsepower for maximumpenetration. The airhammer has little chance of becoming stuck in thebore hole because the hammer provides adequate bore hole circulation, aswell as adequate core sample-carrying circulation.

This invention possesses many other advantages, and has other purposeswhich may be made more clearly apparent from a consideration of the formin which it may be embodied. This form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail, for the purpose of illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense.

Referring to the drawings

FIGS. 1a and 1b, together, constitute a general illustration of acontinuous coring, air drilling system according to the invention, FIG.1b being a downward continuation of FIG. 1a;

FIGS. 2a through 2i together constitute an enlarged, vertical section,as taken on the line 2--2 of FIGS. 1a and 1b, FIGS. 2b through 2iconstituting successive downward continuations of FIG. 2a;

FIG. 3 is a horizontal section through the swivel, as taken on the line3--3 of FIG. 2a;

FIG. 4 is a horizontal section, as taken on the line 4--4 of FIG. 2b;

FIG. 5 is a horizontal section, as taken on the line 5--5 of FIG. 2f;

FIG. 6 is a horizontal section, as taken on the line 6--6 of FIG. 2g;

FIG. 7 is a horizontal section, as taken on the line 7--7 of FIG. 2h;

FIG. 8 is a horizontal section, as taken on the line 8--8 of FIG. 2h;

FIG. 9 is a horizontal section, as taken on the line 9--9 of FIG. 2i;

FIG1 10 is a horizontal section, as taken on the line 10--10 of FIG. 2i;and

FIG. 11 is an enlarged fragmentary detail in vertical section, at thelower end of the airhammer drill, as taken on the line 11--11 of FIG.10, but showing the drilling and coring operation.

As seen in the drawings, the continuous coring system of the invention,as generally shown in FIGS. 1a and 1b, involves a coring swivel adaptoror assembly S having a rotor 10 adapted to rotate in a stator 11 by apower swivel or air motor M, to which air is supplied via a conduit 12.The stator 11 is held against rotation by means 13 in the derrick D,which allows the swivel S to move downwardly, as drilling progresses, asis well known in the case of drilling with power swivels.

Connected beneath the swivel rotor 10, for rotation therewith, is thedual concentric drill pipe P, made up of lengths or stands as thedrilling progresses, and having at its lower end an airhammer assembly Hfor applying successive hammer blows to a core bit B, as the bit B isrotated to drill the well bore W, while taking a continuous core sample,the pieces of which are carried upwardly in the drill pipe by airsupplied through the airhammer H, the other cuttings being carried inthe bore hole annulus to the top of the well, as customary, by the majorportion of the air supplied to the airhammer. The core sample pieces CSare discharged from the coring adaptor swivel into a suitable receiver14.

As is well known in air drilling, the air may be supplied from asuitable compressed air source, not shown, at high volume and pressureto drive the power swivel or motor M, and thus to drive the drill pipeP, as illustrated. If desired, however, the power swivel or motor M maybe eliminated and a Kelly drive may be employed to rotate the drill pipewhile allowing it to progress downwardly during the drilling operation.In other words, the invention is not concerned with the manner ofapplying torque to the drill pipe P, but with adapting the system to cutand carry a continuous core sample to the receiver 14, utilizing thenovel coring swivel adaptor S, the novel dual concentric drill pipe P,and the novel coring bit and airhammer B and H, respectively, wherebythe usual cuttings are effectively removed from the well bore withoutcontaminating the core sample, and the core sample fragments areefficiently carried to the receiver without substantial fallout orblockage of the drill pipe, the core sample being uniform andrepresentative of the earth formation at the bottom of the bore hole atany given time during the drilling operation.

The coring adaptor swivel S is best seen in FIGS. 2a and 3. Moreparticularly, the rotor 10 is revolvable in the stator 11 and has aninternally threaded receptacle 22 for connection at 23 with the rotarydriven pipe 24 which is driven by the power swivel M and which conductsair to the system from the compressed air source on the rig. The rotor10 has an air inlet chamber 25 which communicates with a suitable numberof ports or passages 26 which extend longitudinally through the rotor 10and open at its lower end. The rotor 10 also has another passage 27opening at its lower end and having a laterally extending branch 28opening at the side of the rotor. At its lower end, the rotor isexternally threaded at 29 to receive the internally threaded box 30 ofthe outer pipe P1 of the dual concentric pipe P, which will be describedbelow, and the rotor also threadedly receives at 31 the inner pipe P2 ofthe dual concentric pipe P, the inner pipe P2 communicating with theport 27. A resilient seal ring 32 is disposed in the threaded jointbetween the pipe box 30 and the rotor 10, but a sealing joint such asthat commonly employed in drill pipe tool joints may be employed.

The stator 11 is composed of a horizontally split housing having anupper part 33 and a lower part 34, having peripheral flanges 35interconnected by fastenings 36, these body parts having a cylindricalbore 37 in which the rotor 10 is revolvable. At the upper, inner portionof the body part 33 is an inner peripheral flange 38 which rests on abushing 39 which in turn engages an upwardly facing shoulder 40 on therotor 10. A lock ring 41 carried by the rotor is disposed above theflange 38 to maintain the rotor assembly. Suitable bushings such aslubricated brass bushings 42 and 43 are carried between the rotor andthe stator body parts to minimize friction.

At vertically spaced locations above and below the laterally openingport 28, the body sections 33 and 34 have suitable sealing ring elementsor cups 44 in grooves 45 sealingly engaged with the cylindrical wall ofthe rotor 10 to prevent leakage between the rotor and the stator from anannular chamber 46 formed between the stator body parts 33 and 34,particularly under the high pressure of reverse circulation, whennecessary to flush the well bore.

As been in FIG. 3, the body sections 33 and 34 also provide a tangentialoutlet 47 for the chamber 46, and a coupling 48 has its flanged end 49engaged in a groove 50 in the stator body when the body parts 33 and 34are assembled. This coupling 48 is adapted to be threadedly connected at51 to the conduit 52 through which core sample fragments CS areconducted to the receiver 14.

Adjacent to the location where the port 28 opens into the chamber 46 isa wiper or sample diverter 53 fastened to the rotor 10 by fastenings 54.This wiper conforms in profile to the chamber 46 and has an advancingface 55 angled to gently impart motion to the particles of core samplein a right-hand direction in the chamber 46 and assist the air ininducing movement of the particles to the outlet 47 with a minimum ofbreakage and mixing of the samples.

The continuous coring adaptor pipe or dual concentric pipe P, asindicated above, consists of the outer pipe string P1 and the inner pipestring P2. The outer pipe P1 is typical standard drill pipe and theinner pipe P2 is standard tubing, assembled in a novel manner tominimize problems of assembly, vibration, differential expansion, andthe like, but enabling the lengths of pipe P to be made up and brokenout in the usual manner during the drilling operations.

The dual concentric pipe string P and its interconnection with theswivel S and the airhammer H are illustrated in FIGS. 2a through 2f. Asseen in FIGS. 2a and 2b, means are provided for coupling the pipe P tothe swivel rotor 10 for rotation as a unit. As previously indicated,however, if the rig has a rotary table drive, a Kelly assembly would beinterposed at this location to drive the pipe rotatively, in lieu of thepower swivel or motor M.

The internally threaded box 30 of FIG. 2a has a downwardly extended pipesection 60 threaded at its lower end at 61 to an adaptor sub 62 whichhas at its lower end a typical drill pipe threaded pin 63 engaged in thethreaded box 64 of a tubular coupling member 65 which, in turn, has atits lower end a typical threaded pin 66 at the upper end of a typicallength L of the dual concentric drill pipe or continuous coring adaptorpipe. The inner pipe P2 of FIGS. 2a and 2b includes a length of adaptortubing 68 threaded at 31 with the swivel rotor 10 and extendingdownwardly through the adaptor sub 62 and into the coupling 65. At itslower end, the adaptor tubing 68 is centralized in the coupling 65 by asuitable spider 69, formed in the illustrative embodiment, as a squarebody (FIG. 4) having a square opening 70 through which the tube 68extends. The spider 69 is held against downward movement on the tube 68by a snap ring 71 engaged in a companion groove 72 in the tube 68. Theopenings 73 between the spider 69 and the inside of the coupling 65allow air to flow through the coupling 65 without substantialinterference.

Below the spider 69 the tube 68 has a cylindrical lower end section 74on which is affixed an inner pipe coupling sleeve 75 having an innertubular body 76 of elastomeric material supported within an outer metalsleeve 77, and adapted to have a friction or slip fit at 78 with theinner tube or pipe 80 which is disposed in the box end 67 of the typicallength of dual concentric pipe shown in FIGS. 2b through 2d.

Such a length of dual concentric drill pipe includes the inner tube orpipe 80 and the outer length of pipe 81. The box end 67 of the outerpipe 81 is, as customary, applied as a tool joint to the body of thepipe. At the lower end of the pipe body 81, it is provided with atypical drill pipe tool joint 83 having a threaded pin 84 engageable inthe next below length of drill pipe, as customary.

In the present case, the inner tube 80 is centralized in the outer pipe81 and longitudinally positioned thereon by a suitable number ofvibration absorbing centralizer means 85, the cross sectionalconfiguration of which is seen in FIG. 5. Each centralizer means 85 iscomposed of elastomeric or rubber-like material capable of resilientdeformation. It includes a central tubular body 86 frictionally engagedwith the inner tube 80. Preferably, the body 86 is axially deformedbetween opposed stop rings 87 in companion axially spaced grooves in thetube 80, whereby the body 86 is also radially or circumferentiallydeformed into tight holding engagement with the tube 80 on assembly. Atcircumferentially spaced locations about the centralizer body 86, it haslongitudinally extended radiating ribs 88 frictionally engaged on theouter edge surfaces 89 within the outer pipe 81. Preferably, thediametrical dimension of the ribs 88 is greater than the inside diameterof the pipe 81 to enhance the frictional engagement and compensate forwear, the ribs being radially deformed upon assembly of the drill pipelength L. The ribs 88 afford abundant air flow spaces 90 therebetween.

In order to prevent significant relative longitudinal movement of theinner and outer pipes 80 and 81, moreover, the centralizers 85 at theupper and lower ends of the drill pipe lengths L also are adapted toresiliently position the inner pipe 80 longitudinally with respect tothe outer pipe 81. As seen in FIGS. 2c and 2d, there are threecentralizers 85 in the typical drill pipe length L, each constructed asabove described. However, the upper tool joint 67 and the lower tooljoint 83 are modified, as compared with standard tool joints, to providedownwardly and upwardly facing shoulders 67a and 83a, respectively,engaged by opposing end surfaces 67b and 83b on the ribs 88 of the upperand lower centralizers 85, preferably under compression axially of theassembly. Due to the above described friction or interference fitbetween the centralizers 85, the inner pipe 80 and the outer pipe 81,the pipes are interconnected so as to resist accidental separation, evenafter substantial wear. The resilient centralizer material dampensvibration and reduces shock loads travelling in the drill string.

A suitable number of the drill string lengths L are added to the drillpipe string P, as the drilling progresses, between the coupling 65 andthe uppermost pipe length L, and, except for the lowermost pipe lengthL, each length has, at the lower end of the inner pipe 80, as seen inFIG. 2d, one of the coupling sleeves 75 previously described, affixed tothe cylindrical lower pipe end 80a and adapted to telescopically engageover the upper tubular end 80b of the inner pipe 80 in the length Lbelow. Such a resilient and telescopic connection between the innerpipes 80 not only seals the connection but compensates for tolerancesand some relative longitudinal movement of the pipes 80 and 81.

As seen in FIGS. 2f and 2g, the lowermost length of drill pipe P isconnected to the novel airhammer H, hereinafter to be described. Asshown, the threaded pin 84 of the tool joint 83 is threaded into theinternally threaded box of a top sub 91 for the airhammer H. This topsub 91 has an outer body 92 threaded at 93 at its lower end forconnection with the upper end of the airhammer H. Internally, the subbody 92 has a central tube 94 which sealingly and slidably receives at95 the lower tubular end 96 of the pipe 80 of the above pipe length L.At its lower end the stem 94 has a circumferentially outwardly extendedflange 97 held in place, when the top sub is connected to the hammerassembly H, between the latter and an internal shoulder 98 at the lowerend of the body 92. This flange 97 has a number of circumferentiallyspaced ports 99 (FIG. 6) communicating with the annular space betweenthe body 92 and the tube 94, which annular space communicates, in FIG.2f, with the annular space between the outer pipe P1 and the inner pipeP2 of the drill string P, which then in turn, as seen in FIG. 2a,communicates through the swivel rotor ports 26 with the air inletconduit 24. The tube 94 of the hammer top sub 91, on the other hand,communicates through the inner pipes 80 with the swivel rotor port 27,and thence through the stator chamber 46 of the swivel with the sampledischarge port 47.

The airhammer and bit construction are illustrated in FIGS. 2g through2i.

More particularly, as shown in the drawings, the airhammer apparatus His secured to the lower end of the top sub 91 by a valve body andcoupling 100 by means of which the apparatus is rotated tocorrespondingly rotate an impact anvil bit used for drilling the borehole W and cutting the core, the apparatus delivering repeated impactblows upon the anvil bit when compressed air is forced down the drillpipe annulus for actuating the apparatus and for cleaning the cuttingsfrom the bottom of the hole, and carrying core sample fragments upwardlythrough the inner pipe 80. The apparatus is relatively simple,consisting of an elongate housing structure 110 that includes the upperconnector 100 for threaded attachment to the lower end 93 of the top suband thus to the string of drill pipe that extends to the drilling rig atthe top of the bore hole W. This connector 100 is threadedly secured tothe upper portion of an elongate housing section 114, which can be ofone piece, the lower end of which is threadedly secured to a lowerhousing head or drive member 115, the lower end 116 of the housingsection bearing against an upwardly facing shoulder 117 formed on thehead.

An elongate anvil portion 118 of the anvil bit B is piloted upwardlywithin the drive member 115, a hammer piston 120 being reciprocable inthe housing section 114 above the anvil 118 to deliver repeated impactblows thereagainst. The anvil is preferably formed integrally with thedrill bit portion 121 of the anvil bit, and which has suitable cuttingelements 122, such as sintered carbide buttons, mounted in its drillingface 123 for impacting against the bottom of the bore hole, to producecuttings therein, the cutting elements 122 also acting against the sideof the bore hole adjacent to its bottom to insure the production of abore hole W of the desired diameter.

As best seen in FIGS. 10 and 11, the bit also has an inner circular setof cutting elements 122a disposed in spaced relation about a centralopening 122b in which is a cutter ring 122c of sintered carbide, or thelike, for cutting a core sample, as will be later described.

During the reciprocation of the hammer piston 120 in the housing todeliver impact blows upon the anvil bit, the drill pipe string P andhousing structure 100 are rotated at a desired speed, such as 20 r.p.m.,by the power swivel M or by a rotary table drive, to correspondinglyrotate the anvil bit B and insure an impacting action of the cuttingmembers 122 and 122a over substantially the entire cross-sectional areaof the bottom of the hole, except for the central area within the member122a. During the impacting action, suitable drilling weight is imposedon the anvil bit through the drill pipe string P and the housingstructure 110, such drilling weight being transferred from the lower end124 of the housing head or drive member 115 to an upwardly facingshoulder 125 of the bit 121. The rotary drive itself is transferred fromthe housing structure 110 to the anvil 118 through a slidable splinetype of connection 126, FIG. 9 and FIG. 2i.

In general, the upper portion of the anvil has circumferentially spacedelongate recesses 127 in which drive segments 128 are disposed, thesesegments being carried in circumferentially spaced windows 129 in thedrive member 115. The recesses 127 are substantially longer than thelength of the segments 128, permitting relative longitudinal movement ofthe anvil bit B with respect to the housing structure 110. The rotaryeffort is transferred from the housing section 114 to the drive member115 by virtue of the threaded connection 130d, and from the sides 129aof the openings or windows 129 to the segments 128, from where theturning effort is transmitted through the abutting segment surfaces 127aon the segments 128 to the anvil.

The housing section 114 includes an elongate, upper, inner cylindricalhousing wall 130, the lower end 131 of which constitutes an upperhousing flow control corner at the upper end of an elongate internalcircumferential exhaust groove 132 of a larger internal diameter thanthe sub-jacent inner cylindrical housing wall 134, which may be of thesame internal diameter as the upper housing wall 130, the upper end ofthe lower wall 134 providing a lower flow control corner 133. The lowerend 135 of the wall 134 provides a by-pass corner at the upper end of anenlarged internal diameter circumferential by-pass groove 136.

The hammer piston 120 includes an upper piston portion 137 having anexternal diameter 137a conforming to the diameter of the upper innercylindrical housing wall 130, this upper piston portion terminating atthe upper end 138 of an external, reduced, circumferential exhaustgroove 139. This groove 139 terminates at a lower piston portion 140having an external diameter conforming to the internal diameter of thelower inner cylindrical housing wall 134. Below its lower piston portion140, the hammer is of a reduced external diameter 141 to provide an airpassage and the lower end has guide ribs 142 which, upon removal of theanvil bit from the housing 110, engage a limit ring 143 mounted in thehousing section 114 to prevent the piston 120 from dropping from thehousing structure.

Above its upper piston portion 137, the hammer portion 120 has aplurality of relief spaces 144 (FIG. 7) extending from the upper pistonportion 137 to the upper end 146 of the piston, there being spacedelongate arcuate sections 147 slidably engaging the wall 130.

When the hammer piston 120 is at the lower end of its stroke, as shown,a flow control piston corner 150 at the upper end of the piston portion137 is spaced below the upper housing flow control corner 131, allowingair in the housing above the piston 120 to flow down through thepassages 144 and into the internal circumferential exhaust groove 132,around the upper piston portion 137, then into radial exhaust ports 151formed in the hammer piston below an intermediate annular barrier wall152 that communicate with an elongate central piston cavity 153, intowhich an exhaust tube 154 extends upwardly from the anvil 118, the tubeforming a continuation of the exhaust passage 153 and communicating withan annular exhaust passage 155 through the anvil and through one or aplurality of exhaust passages 156 extending downwardly through the bit121 and opening outwardly thereof for the purpose of enabling thedrilling fluid to flow into the bore hole W for removing cuttings fromthe bottom of the hole. The tube 154 makes a slidable seal with the wall153a of the piston cavity 153, being secured to the anvil 118 by a loweroutwardly extending flange 157 received within an inner circumferentialgroove 158 in the anvil. The tube may be made of an elastic material,such as Delrin, which permits it to be inserted within the anvilpassage, the flange 157 contracting sufficiently until it is oppositethe circumferential groove 158.

Disposed in the airhammer is a tubular core tube and air tube assembly101, including an inner core tube 102 and an outer air tube 103. Thecore 102 extends from adjacent the lower end of the bit 121 above thecentral opening 122b, upwardly through the connector or valve housing100 into a socket 100a in the latter, so as to communicate with centraltube 94 in the top sub 91, and, thus, with the inner pipe 80 of the dualconcentric drill pipe string P leading to the swivel S. The air tube 103is disposed about the core tube 102 in spaced relation thereto, and hasan upper end flange 104 engaged in a companion groove in a reversingvalve tube 178 to be later described. Here again, the tube 103 may be ofresilient material adapted to snap into engagement with the valve tube178, when inserted into the socket 178b. The tube 103 engages within theintermediate piston wall 152. At the lower end of the core tube 102 andair tube 103, they are provided with a retainer ring 105 and seal 106'below a number of air ports 107 which extend at an angle inwardly andupwardly from the lower end of the annular space 106 between the tubes102 and 103 into the core tube 102 just above its open, lower endadjacent to the bottom of the bit 121. At its upper end, the air tube103 is connected to the valve tube 178, the upper end of which has aflange 108 engageable in a groove in the socket 108a in the connectorand valve body 100. The structure and function of the valve tube 178, inreversing the hammer piston, will be later described.

When the piston 120 is shifted upwardly within the housing on its returnstroke, the return air corner 160 at the lower end of the lower pistonportion 140 will be disposed above the housing lower flow control corner133, whereupon the compressed air below the piston can exhaust into theinternal circumferential housing groove 132 and flow through the exhaustports 151 and exhaust passages 153, 155 and 156 to the bottom of thebore hole. At this time, the upper flow control piston corner 150 willbe disposed above the upper housing flow control corner 131, which willseal the upper piston portion 137 against the upper inner cylindricalhousing wall 130, whereupon compressed air can drive the piston 120downwardly on its hammer or power stroke. When the return air corner 160moves below the housing lower flow control corner 133, the air below thepiston and within the housing, which remains after the lower pistonportion 140 is closed within the lower end of the cylindrical housingwall 134, is subject to compression, but such air will be at arelatively low pressure.

Compressed air for reciprocating the hammer piston 120 passes downwardlythrough the annulus provided in the string of drill pipe P and into theupper housing sub 92, flowing through the ports 99 past a downwardlyopening check valve 170 which may be in the form of a ring 171 receivedwithin a bore 172 in the connector 100, the ring 171 having a resilientvalve head 173 movable upwardly to engage beneath the flange 97 by acoiled spring 175 which seats on a shoulder 175a in the connector 100.Downward movement of the valve ring 171 is limited by its engagementwith an intermediate shoulder 176 in the body 100. With air being pumpeddownwardly through the apparatus, the valve 170 is unseated and the aircan flow between the ring 171 and the core tube 102, into the annulus177 defined between the valve tube 178 and the core tube 102.

The inlet air under pressure is caused to flow alternately into thehousing below the piston 120 and the housing above the piston, to effectreciprocation of the hammer, by the reversing valve tube 178, whichseparates an upper annular air chamber 179 from the lower air chamber153.

The piston 120 has an elongate upper cylindrical surface 182 openingthrough its upper end 146 and terminating at an inner, flow controlpiston corner 183, which is the upper end portion of an elongateinternal circumferential impact passage groove 184 having a largerinternal diameter than the inside diameter of the upper piston portion182. The impact passage groove 184 terminates at an intermediate innercylindrical piston wall 185, which may have the same internal diameteras the upper cylindrical piston wall 182, the intermediate wallterminating at an internal circumferential return passage groove 186formed in the piston and terminating at a lower flow control pistoncorner 187, which is the upper end of a lower internal piston seal wallportion 188 that forms a bore extending between the intermediate pistonwall 152 and the corner 187. The inlet tube 178 has an upper externalcylindrical sealing portion 189 having labyrinth seal grooves 189a,relatively sealingly slidable within the upper piston wall 182 andterminating in an external circumferential inlet groove 190communicating with radial inlet ports 191 that open to the centralannular inlet passage 192 between the valve tube 178 and core tube 102.Below this inlet groove 190, the tube 178 is formed with an intermediatecylindrical sealing section 193 having labyrinth seal grooves 193aslidably and sealingly engageable with the intermediate innercylindrical piston wall 185 and also with the lower piston wall 188.

When the piston 120 is in its lowermost operative position, with thedrill bit 121 pressed against the bottom of the bore hole W, compressedair can flow downwardly through the inlet passage 192, discharging intothe return passge 186 that communicates with the upper portion of one ormore longitudinal return passages 195 extending downwardly through thehammer piston and opening outwardly through its lower end 196. When thehammer piston 120 moves upwardly within the housing 110 and along theinlet tube 178, the cylindrical piston wall 185 seals with the sealingsection 193 of the tube 178 to interrupt communication between the inletpassage 192 and the return passages 195, continued upward movement ofthe piston then placing the inner upper flow control piston corner 183above the upper flow control valve tube corner 198, which then allowscompressed air to flow from the inlet passage 192 through the ports 191into the circumferential inlet groove 190 and into the internalcircumferential impact passage groove 184, and thence into the housingabove the upper end 146 of the piston. At this time, the upper pistonportion 150 will have moved partially above the upper housing flowcontrol corner 131, so that the air under pressure between the upper end146 of the piston and the connector 100 can act downwardly on thepiston, urging it in a downward direction.

The piston 120 thus will be shifted downwardly until the upper flowcontrol piston corner 183 moves below the flow control housing tubecorner 198, which shuts off air pressure into the housing above thepiston, the piston continuing to move downwardly, as the compressed airexpands, until the outer upper flow control piston corner 150 movesbelow the upper housing flow control corner 131, which then permits airabove the piston to pass through the passages 144 into the internalcircumferential exhaust passage 132, and through the exhaust ports 151and exhaust passages 153, 155 and 156 to the bottom of the hole belowthe drill bit, the hammer piston being driven against the upper face118a of the anvil to deliver an impact blow to the impact bit B. As thepiston 120 nears the end of its downward stroke, the cylindrical sealingwall 185 of the piston moves below the valve tube sealing section 193,thereby allowing the compressed air to flow from the inlet passage 192into the upper piston cavity 179 and internal circumferential returnpassage groove 186, passing downwardly through the longitudinal returnpassages 195 to the lower end of the piston, such air then moving thepiston in an upward direction, until the piston wall 185 passes upwardlyinto sealing relation to the valve tube wall 193 once again, to shut offthe flow of air into the return passage 195. When this occurs, the outerupper flow control piston corner 150 moves above the upper housing flowcontrol corner 131 to shut off the exhaust of air from the housingregion above the piston 120, the compressed air below the pistonexpanding and driving the hammer piston upwardly toward the connector100. Before the hammer reaches the connector 100, the inner upper flowcontrol piston corner 183 will have shifted upwardly along the tube 178to a position above the upper flow control housing tube corner 198,allowing air under pressure to pass from the inlet passage 192 throughthe impact passage grooves 190, 184 to a position in the housing abovethe piston 120.

The upward travel of the piston 120 is cushioned by the compression ofthe air remaining in the housing above the piston. However, the pistonwill still move upwardly sufficiently to place the lower corner 160 ofthe lower piston portion 140 above the housing lower flow control corner133, which then permits the compressed air below the piston to travelinto the internal circumferential exhaust groove 132 and through theexhaust ports 151 into the exhaust passages 153, 155 and 156 fordischarge from the drill bit. The compressed air in the housingstructure above the piston then expands to drive the piston downwardly,and the foregoing cycle of operation is repeated, the pistonreciprocating to deliver repeated impact blows against the anvil portion118 of the anvil bit B, while the drill string P is being rotated, toinsure that the drilling or cutting elements 122, 122a will coversubstantially the entire cross-sectional area of the bore hole bottom.

As seen in FIGS. 2i and 11, the cutters 122a are adapted to form a core200 at the center of the bottom of the bore hole, the core beinggenerally frusto-conical in shape. As the cutter ring 122c progressesdownwardly, it will trim the core 200 and forms with the core a sealwhich is adapted to preclude entry of other earth particles into thecore passage 122b. As drilling progresses, the upper portion of the corewill break off or fragment, as indicated at CS, to produce core samplefragments which are clean and representative of the bore hole bottom,without contamination by sidewall cuttings or debris.

These core samples CS are carried upwardly through the core tube by aportion of the air being circulated to effect reciprocation of thehammer. Again, referring to FIGS. 2g through 2i, it will be noted thatthe annular space 106, between the core tube 102 and the air tube 103,which communicates with the ports 107 at the bottom of the core tube102, also is in open communication with the annulus 177 between the coretube 102 and the valve tube 178. The flow restriction of the annulus 106and the ports 107 is such, as compared with the lesser restrictions toair flow in the hammer operating system, that the major portion of theair is utilized to operate the hammer and flush cuttings upwardly in thebore hole W, and the minor portion of the air is utilized to carry thecore samples upwardly in the core tube 102 and on up to the swivelchamber 46 through the inner pipe 80 of the dual concentric drill pipe,at high velocity.

The core sample fragments are carried through the drill pipe and aredischarged into the swivel chamber 46, where the air and the revolvingpusher 53 carry them to the outlet 47 for collection as described above.

From the foregoing, it will be apparent that the invention provides anovel and advantageous system for continuously taking a core samplewhile drilling with a percussion type core bit, which efficiently makesuse of the available air for removing cuttings from the well bore andtransporting the core sample fragments to the top of the well. The novelswivel S enables the core samples to be recovered with a minimum ofdamage or breakage, due to the gentle direction changes in the path ofthe fragments. The dual concentric drill pipe is simple in itsconstruction, easy to assembly and facilitates utilizing typical welldrilling pipe, as well as make up and break out tongs, when adding orremoving lengths to and from the drill string. The novel airhammerdrill, with its air dividing means and core cutting arrangement in thebit enable clean samples to be taken and carried to the surface at highvelocity and uniformly without gravity separation, so that the samplesare representative of the formation being drilled through at any giventime.

We claim:
 1. A dual concentric drill pipe for continuously taking coresamples from the bottom of a bore hole while drilling progresses;comprising inner and outer pipe sections defining an annular spacetherebetween, said outer pipe section having opposite ends provided withtool joints adapted to be connected to adjacent corresponding outer pipesections, said inner pipe section having at one end a cylindricalsection and at the other end telescopic coupling means frictionallyengageable with the cylindrical end of an adjacent inner pipe section,and means resiliently centralizing said inner pipe section in said outerpipe section; said centralizer means comprising an elastomeric element,said element including a cylindrical sleeve mounted on said inner pipesection and circumferentially spaced ribs extending from said sleeve andfrictionally engaging said outer pipe section, and means engaging onsaid inner pipe section and the ends of said sleeve to axially compresssaid sleeve and retain said sleeve in a compressed condition on saidinner pipe section.
 2. A dual concentric drill pipe as defined in claim1; said centralizer means comprising a plurality of longitudinallyspaced elastomeric elements, each of said elements including saidcylindrical sleeve mounted on said inner pipe section andcircumferentially spaced ribs extending from said sleeve andfrictionally engaging said outer pipe section, the ribs of each elementbeing of initial radial dimension greater than the radial distancebetween said cylindrical sleeve and outer pipe section and beingcompressed between said inner and outer pipe sections, said meansengaging said inner pipe section and the ends of each of said sleeves toaxially compress said sleeves and retain said sleeves in a compressedcondition on said inner pipe section.
 3. A dual concentric drill pipe asdefined in claim 1; said ribs being of initial radial dimension greaterthan the radial distance between said cylindrical sleeve and outer pipesection and being compressed between said inner and outer pipe sections.4. A dual concentric drill pipe as defined in claim 1; said telescopiccoupling means comprising an elastomeric coupling sleeve frictionallyengageable with the cylindrical end of the adjacent inner pipe section,and a reinforcing sleeve embracing said elastomeric coupling sleeve. 5.A dual concentric drill pipe for continuously taking core samples fromthe bottom of a bore hole while drilling progresses; comprising innerand outer pipe sections defining an annular space therebetween, saidouter pipe section having opposite ends provided with tool jointsadapted to be connected to adjacent corresponding outer pipe sectionsand an inner cylindrical wall between said tool joints, and inner pipesection having at one end a cylindrical section and at the other endtelescopic coupling means frictionally engageable with the cylindricalend of an adjacent inner pipe section, and means resilientlycentralizing said inner pipe section in said outer pipe section; saidcentralizing means comprising a plurality of longitudinally spacedelastomeric elements mounted on said inner pipe section and frictionallyengaging said cylindrical wall of said outer pipe section; axiallyspaced shoulders on one of said pipe sections adjacent said cylindricalwall and adjacent the end portions of said one pipe section, means onsaid other pipe section engaging said elements located adjacent saidshoulders to compress said last-mentioned elements against saidshoulders to resist relative axial movement between said inner and outerpipe sections.
 6. A dual concentric drill pipe as defined in claim 5;each of said elements including a cylindrical sleeve mounted on saidinner pipe section and circumferentially spaced ribs extending from saidsleeve and frictionally engaging said outer pipe section, the ribs ofeach element being of initial radial dimension greater than the radialdistance between said cylindrical sleeve and outer pipe section andbeing compressed between said inner and outer pipe sections; saidaxially spaced shoulders being on said outer pipe section adjacent theend portions of said outer pipe section.
 7. A dual concentric drill pipeas defined in claim 5; said axially spaced shoulders being on said outerpipe section adjacent the end portions of said outer pipe section saidtelescopic coupling means comprising an elastomeric coupling sleevefrictionally engageable with the cylindrical end of the adjacent innerpipe section, and a reinforcing sleeve embracing said elastomericcoupling sleeve.
 8. A dual concentric drill pipe for continuously takingcore samples from the bottom of a bore hole while drilling progresses;comprising inner and outer pipe sections defining an annular spacetherebetween, said outer pipe section having opposite ends provided withtool joints adapted to be connected to adjacent corresponding outer pipesections, said inner pipe sections having at one end a cylindricalsection and at the other end telescopic coupling means frictionallyengageable with the cylindrical end of an adjacent inner pipe section,and means resiliently centralizing said inner pipe section in said outerpipe section; said centralizing means comprising a plurality oflongitudinally spaced elastomeric elements mounted on said inner pipesection and frictionally engaging said outer pipe section; axiallyspaced shoulders on one of said pipe sections adjacent on end portionsof said one pipe section, said elements adjacent said shoulders engagingand being compressed against said shoulders to resist relative axialmovement between said inner and outer pipe sections; each of saidelements including a cylindrical sleeve mounted on said inner pipesection and circumferentially spaced ribs extending from said sleeve andfrictionally engaging said outer pipe section, the ribs of each elementbeing of initial radial dimension greater than the radial distancebetween said cylindrical sleeve and outer pipe section and beingcompressed between said inner and outer pipe sections, and meansengaging said inner pipe section and the ends of each of said sleeves toaxially compress said sleeves and retain said sleeves in a compressedcondition on said inner pipe section; said axially spaced shouldersbeing on said outer pipe section adjacent the end portions of said outerpipe section.
 9. A dual concentric pipe as defined in claim 8; saidtelescopic coupling means comprising an elastomeric coupling sleevefrictionally engagable with the cylindrical end of the adjacent innerpipe section, and a reinforcing sleeve embracing said elastomericcoupling sleeve.